|Publication number||US7581041 B1|
|Application number||US 10/749,325|
|Publication date||Aug 25, 2009|
|Filing date||Dec 29, 2003|
|Priority date||Dec 29, 2003|
|Also published as||US8195864, US8606986, US20090077298, US20120236872, US20140189188|
|Publication number||10749325, 749325, US 7581041 B1, US 7581041B1, US-B1-7581041, US7581041 B1, US7581041B1|
|Inventors||Colin Whitby-Strevens, Michael D. Johas Teener|
|Original Assignee||Apple Inc.|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (13), Non-Patent Citations (18), Referenced by (8), Classifications (11), Legal Events (3)|
|External Links: USPTO, USPTO Assignment, Espacenet|
The present invention relates broadly to devices connected to a high-speed serial bus. Specifically, the present invention relates to bridging data transmission between IEEE 1394-compliant devices and Ethernet-compliant devices.
A “bus” is a collection of signals interconnecting two or more electrical devices that permits one device to transmit information to one or more other devices. There are many different types of buses used in computers and computer-related products. Examples include the Peripheral Component Interconnect (“PCI”) bus, the Industry Standard Architecture (“ISA”) bus and the Universal Serial Bus (“USB”), to name a few. Bus operation is usually defined by a standard that specifies various concerns such as the electrical characteristics of the bus, how data is to be transmitted over the bus, how requests for data are acknowledged, and the like. Using a bus to perform an activity, such as transmitting data, requesting data, etc., is generally called running a “cycle.”Standardizing a bus protocol helps to ensure effective communication between devices connected to the bus, even if such devices are made by different manufacturers. Any company wishing to make and sell a device to be used on a particular bus, provides that device with an interface unique to the bus to which the device will connect. Designing a device to particular bus standard ensures that device will be able to communicate properly with all other devices connected to the same bus, even if such other devices are made by different manufacturers.
Thus, for example, an internal fax/modem (i.e., internal to a personal computer) designed for operation on a PCI bus will be able to transmit and receive data to and from other devices on the PCI bus, even if each device on the PCI bus is made by a different manufacturer.
Problems occur when devices located on buses or networks using different low-level protocols are made to communicate with each other. One example involves two very popular standards, the IEEE 1394 family of serial bus protocols, and the IEEE 802.3 family of Ethernet network protocols. Despite the fact that there are versions of both protocols that use the same cables and connectors, and both support the higher level “Internet Protocol” (IP), devices implementing the Ethernet-compliant network interface are unable to communicate with devices implementing the 1394-compliant bus interface because of the differences existing between the respective protocols. Because of the large number of existing devices that use one protocol or the other, this communication gap is likely to widen as standards are developed in the two protocols. Thus, there is a heartfelt need for a solution that bridges the communication gap between protocols and effectively allows devices to communicate with each other across different bus or networking architectures.
The present invention solves the problems discussed above by providing a method and apparatus for communicating data between a gigabit Ethernet architecture and a IEEE 1394-compliant architecture. In an embodiment, the present invention provides a hub device that incorporates a 1394-compliant physical layer and an Ethernet physical layer and bridges communication between the two architectures at the Internet Protocol layer.
In another embodiment, the present invention provides a method of communicating data between an Ethernet system and a 1394-compliant system by transmitting an S800 1394b stream within a 1000 BASE-T transmit stream by inserting an illegal 1394b symbol into the stream approximately once for every 59 regular symbols transmitted in the 1000 BASE-T transmit stream. This illegal symbol is inserted to compensate for the fact that the bit rate for S800 after an 8B10B encode is 983.04 Mbps+/−100 ppm, and the bit rate for 1000 BASE-T stream is slightly faster at 1000 Mbps+/−50 ppm. The illegal symbol can be inserted into the transmit stream at a fixed rate, or in another embodiment, by utilizing a one-symbol queue that is fed by a 1394b transmitting port and drained by logic which supplies it to the 1000 base Tx PHY. In this embodiment, when the queue underflows, the illegal symbol is generated by the logic which drains the queue. To receive a 1394-compliant stream over an Ethernet bus, the same approach can be followed. The illegal symbols received are recognized and ignored. In an embodiment, a receive FIFO is centered when the start of a packet is recognized, i.e. enough symbols are buffered to allow for the jitter in the arrival rate resulting from deleting the illegal symbols, and also to compensate for ppm clock differences which might result in symbols being placed in the FIFO at a slower rate than they are removed.
In another aspect of the present invention, an autonegotiation process executes to select either an Ethernet protocol or a 1394b protocol to be used on a connected communication medium. In this manner, data from a gigabit Ethernet architecture, or data from a 1394-compliant architecture, can be transmitted across a common medium, without any manual configuration required of a user. In this embodiment, five registers are included on a 1394b PHY, but the port in the 1394b PHY runs off the same 125 MHz clock as is provided by the gigabit media independent interface (GMII). A modulo 5 counter is included on the 1394b PHY to control symbol insertion into the transmit queue located on the 1394b side. The modulo 5 counter iteratively counts from 0 to 4. If the modulo 5 counter has a zero value, then the 1394b side does not push a 10-bit number into the FIFO. For cases where the counter has a non-zero value, the 1394b side pushes the 10-bit symbol assembled to preserve clock consistency across different clock domains.
In yet another aspect, the present invention provides a method of transmitting data across a high-speed serial bus. In accordance with an IEEE 1394-compliant PHY's TX symbol clock, a 10-bit symbol is generated on an IEEE 1394-compliant PHY. The 10-bit symbol is scrambled and encoded and placed in a FIFO. In accordance with an IEEE 802.3-compliant PHY's TX clock, the 10-bit symbol is removed from the FIFO, an 8-bit byte is derived from the removed 10-bit symbol; and sent to an IEEE 802.3-compliant PHY. A symbol is removed from the FIFO on four out of every five GMII TX clock cycles. A null 10-bit symbol is placed in the FIFO if there are no 10-bit symbols present in the FIFO. The modulo 5 counter is used to derive the 8-bit byte in the following manner: First, the 8-bit byte is derived from the 10-bit symbol by using 8 bits from the extracted 10-bit symbol, and the two remaining bits are stored. The next 8-bit byte is derived by extracting from the FIFO a second 10-bit symbol and assembling an 8-bit byte from the stored two bits and six bits from the extracted second 10-bit symbol, the four remaining bits from the extracted second symbol are stored and the second 8-bit byte is sent to the IEEE 802.3-compliant PHY. A third 8-bit byte is derived by extracting from the FIFO a third 10-bit symbol and assembling an 8-bit byte from the four stored bits and four bits from the third extracted symbol. The six remaining bits from the extracted third symbol are stored and the third 8-bit byte is sent to the IEEE 802.3-compliant PHY. A fourth 8-bit byte is derived by extracting from the FIFO a fourth 10-bit symbol, and assembling an 8-bit byte from the six stored bits and 2 bits from the extracted fourth 10-bit symbol. The eight remaining bits from the extracted fourth symbol are stored and the fourth 8-bit byte is sent to the IEEE 802.3-compliant PHY. A fifth 8-bit byte is derived from the stored eight remaining bits and sent to the IEEE 802.3-compliant PHY.
On the receiving side, the method comprises receiving an 8-bit byte, and in accordance with a GMII RX clock, if the received 8-bit byte contains a null symbol, then deleting the null symbol; else storing the 8-bit byte in a first register; receiving a second 8-bit byte that does not contain a null symbol and storing it in a second register. A 10-bit symbol is assembled from the 8-bit byte stored in the first register and appending two bits from the 8-bit byte stored in the second register. The assembled 10-bit symbol is placed in a first FIFO. In accordance with a second clock, the 10-bit symbol is removed from the first FIFO. 8B10B and control decoding is performed on it before it is placed in a second FIFO. In accordance with a third clock, the decoded 10-bit symbol is removed from the second FIFO; and sent to an IEEE 1394-compliant PHY. The frequency of null character deletion is used to control a phased locked loop associated with the second clock.
In still another aspect, the present invention provides a method of transmitting data across a high-speed serial bus, comprising: in accordance with a first TX symbol clock: generating a 10-bit symbol on an IEEE 1394-compliant PHY having a port interface, placing the generated 10-bit symbol on the port interface, performing flagged encoding the 10-bit symbol, and placing the 10-bit symbol in a FIFO. In accordance with a second TX clock, the 10-bit symbol is removed from the FIFO, an 8-bit byte is derived from the removed 10-bit symbol; and sent to an IEEE 802.3-compliant PHY.
In yet another aspect, the present invention provides an apparatus for transmitting data across a high-speed serial bus, the method comprising: an IEEE 802.3-compliant PHY having a GMII interface; an IEEE 1394-compliant PHY in communication with the IEEE 802.3-compliant PHY; a first connection, the first connection for transmitting data between a device and the IEEE 802.3-compliant PHY; and a second connection, the second connection for transmitting data between a device and the IEEE 1394-compliant PHY. The IEEE 1394-compliant PHY is in communication with the IEEE 802.3-compliant PHY via a switch. The switch determines whether data transmission is be routed to the IEEE 802.3-compliant PHY or the IEEE 1394-compliant PHY. An autonegotiation mechanism determines whether data is to be routed between the IEEE 802.3-compliant PHY and the IEEE 1394-compliant PHY, or whether data is to be routed through the IEEE 802.3-compliant PHY to the first connection.
Other features and advantages of the present invention will become apparent from reading the following detailed description, when considered in conjunction with the accompanying drawings.
Various embodiments of the present invention utilize a 1000 BASE-T PHY that transmits and receives at no less than 0.9999 gbit/sec, and a 1394b PHY having a cable interface that utilizes a bit stream rate of no more than 0.98304+100 ppm=0.9831383 gbit/sec. Thus, the fastest S800 1394b transmission rate can be accommodated by the slowest 1000 BASE-T stream.
In an embodiment, the present invention upshifts an S800 1394b stream by inserting an illegal symbol within the transmit stream approximately once for every 59 regular symbols. In an embodiment, the illegal symbol is either all ones or all zeros since those are the furthest Hamming distance from 1394b control symbols or data symbols. In various embodiments, insertion of this illegal symbol can be performed at a fixed rate, or by utilizing a one-symbol FIFO that is fed by the 1394b transmitting port and drained by the 1000 base TX PHY. In this embodiment, when the FIFO underflows, the extra symbol is generated. On receive, the same approach can be followed. In an embodiment, a FIFO is centered at the start of a packet.
In another embodiment of the present invention, the 1000 base-T transmit stream requires a number of Ethernet IDLE symbols to appear periodically. A small transmit FIFO is provided and, when it underflows, transmission of the 1394b symbols is halted and the 1000 base TX PHY is instructed to transmit Ethernet IDLE symbols for 11 Ethernet symbol times. During this time, the transmit FIFO is filling. After the 11 Ethernet symbol times has passed, transmission of 1394b symbols is resumed. Insertion of these idle symbols satisfies a requirement for 1000 base T transmission.
Directing attention to
Directing attention to
Directing attention to
For translation of data in the opposite direction, where 10-bit symbols are formed from 8-bit characters, synchronization characters (i.e. illegal characters) force the value of modulo 5 counter 206 to zero and hold it there. The first valid 8-bit character that is received via connection 120 is copied into register 208 with the counter value still at zero, so the 1394 side of port 114 takes no action. The next 8-bit character received over connection 120 is placed in register 210. The 1394 side of port 114 assembles a 10-bit symbol by taking the eight bits from register 208, appending two bits from register 210, and treating the resulting 10-bit symbol as if it had been received on 1394b port 108. Most such symbols are pushed into the bport RX FIFO, while others, such as repeated request or control symbols, and illegal symbols are ignored. RX Adaptation module 222 deletes the null or illegal 10-bit symbols, and uses the deletion frequency to control the RX symbol clock phase locked loop. Thus, the RX symbol clock is phase locked to the TX symbol clock. Elasticity FIFO 224 compensates for ppm differences between the two PHY clocks. The resulting 10-bit symbol is pushed into FIFO 116, where conventional 1394b deletable symbols functionality prevents bport FIFO underflow and overflow. In an embodiment FIFO 116 is sized slightly larger than FIFO 110 to compensate for the “4inarushthenawait” symbol arrival characteristics. The remaining bits from register 210 are then stored in register 208, and the next 8-bit byte received is stored in register 210. Assembly of 10-bit symbols continues by using all of the bits from register 208, and appending any bits needed from register 210 to form the 10-bit symbol. This 10-bit symbol process continues until register 210 is emptied upon appending bits, at which point the process repeats itself by storing an 8-bit byte in both registers 208, 210 again.
The relationship between 10-bit symbols and 8-bit characters can be conceptualized as illustrated in
In an embodiment of the present invention, training and operation symbols are transmitted to support scrambler synchronization and a port synchronization handshake and can utilize K28.5 substitution. Rather than GHz logic, or phase locked loops, the present invention utilizes single clock synchronous logic in the receiver on PHY 106. Bytes are presented to port 114 from GMII interface 104 synchronously to GMII interface 104's RX clock (running at 125 MHz, in an embodiment), and, unlike conventional 1394b ports, there is no requirement for any high-speed bit receive logic or clock recovery in port 114. The K28.5 symbol in the IBM 8B10B code is a symbol used in normal operation that contains a special “comma” pattern sequence, denoted as 0011111 or 110000, depending on disparity. When a receiver initializes upon start up, it is unaware of where the 10-bit boundaries occur in an incoming bit stream. But when it recognizes a received K28.5 symbol (the comma sequence), it can use this symbol to determine the 10-bit boundary, and thus acquire symbol synchronization. 1394b-compliant devices perform symbol synchronization by performing K28.5 substitution, replacing D28.0 symbols with K28.5 symbols. The receiver uses the K28.5 symbol to acquire symbol synchronization, and also substitutes back the D28.0 symbol for any K28.5 symbols it finds in the stream. 1394b-compliant devices send a training symbol request as the first symbol on a port. This training symbol is scrambled, and the resulting 8B10B data symbol is transmitted. Scrambling the training symbol ensures that periodically the received data symbol is a D28.0 symbol, and the K28.5 substitution can be performed.
When port 114 has acquired symbol and scrambler synchronization, it changes the symbol it is transmitting to an operation symbol. This operation symbol conveys another request, and is scrambled onto 8B10B data symbols in just the same way. As a result of scrambling, a D28.0 symbol is still due to be transmitted occasionally, and K28.5 substitution is performed.
When port 114 is both transmitting and receiving operation request symbols, it is synchronized to its peer node, and also made aware that the peer node is synchronized to port 114. Port training is now considered complete, and port 114 is ready to transmit requests, control symbols, and data in its support of the 1394 protocols. The 5-to-4 relationship between states on the 1394b side and states on the GMII side of port 114 can be illustrated in
Clocking appears as shown in Table 1.
100 MHz clock
phase offset needed <
In an embodiment, illegal symbols are transmitted after the 0 modulo 5 symbols have been transmitted since the last illegal symbol was transmitted, and are also used to synchronize the four 10-bit registers on the 1394b side with the five 8-bit registers on the GMII side. Read and write clock pulses are aligned with the necessary phase offset for the first symbol received after a synchronizing symbol, and the read and write selectors reset to point to register “a” for write and register “ab” for read. The first 10-bit symbol is read one read clock pulse later, after values have been written to both registers a and b. While the four 10-bit registers and five 8-bit registers are synchronizing with each other, no symbols are read out, nor are any 10-bit symbols pushed into the bport RX FIFO using the 100 MHz clock.
The present invention implements the 8-bit GMII interface 104 as a serial interface, by shifting a byte into the 10-bit register on the 1394b side using serial interface FIFO 200. Whenever an illegal symbol is shifted into 10-bit register, it is deleted from FIFO 200. The illegal symbol can be inserted into any stream, and deleted at the other end, even without byte/symbol synchronization.
Directing attention to
Directing attention to
The receive side in this embodiment is similar to the receive side illustrated in
While numerous methods and apparatus for transmitting 1394-compliant symbols using a gigabit Ethernet PHY have been illustrated and described in detail, it is to be understood that many modifications may be made to embodiments of the present invention without departing from the spirit thereof.
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|U.S. Classification||710/52, 710/60, 710/62, 709/233, 710/30, 710/307, 710/68|
|Cooperative Classification||G06F2213/0012, G06F13/4027|
|May 10, 2004||AS||Assignment|
Owner name: APPLE COMPUTER, INC., CALIFORNIA
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Owner name: APPLE INC., CALIFORNIA
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